Zeolite Synthesis From Coal Fly Ash

A huge amount of coal fly ash (CFA) is discharged from electric power plants throughout the world every year.The major application of the coal fly ash is the use for cement or concrete manufacturing.However, this application is limited within the demand of the building requirements.Recently, zeolite synthesis from coal fly ash has been receiving more attention.In this study, several zeolites such as zeolite NaP1, zeolite NaA and zeolite NaX were synthesized by convertional hydrothermal method and microwave supplement multi-stage synthesis technology.The effects of hydrothermal alkaline conditions and additives on the cation exchange capacity (CEC) values of zeolites were investigated.The effect of Si/Al molar ratio of the reactants on the type of zeolite was also discussed. The major conclusions are:(1)The CEC values of zeolites were greatly dependent on the hydrothermal conditions such as reactive temperature, reactive time, liquid/solid ratio and the concentration of sodium hydroxide.The optimal conditions for zeolite synthesis by convertional method were found to be 120℃of temperature, 6h of time, 8.0mL/g of liquid/solid, 2mol/L of NaOH.The CEC values of NaP1, NaA and NaX are 175.9mmol/100g,163.8mmol/100g and 178.3mmol/100g, respectively.(2)The CEC values of zeolite products were improved remarkably by the additives such as NaF, cetyl trimethyl ammonium bromide(CTAB) and 95% ethanol.(3)The type of the products is decided by the Si/Al molar ratio of the coal fly ash, which can be adjusted by addition of NaAlO2.(4)The microwave supplement multi-stage synthesis technology plays an important role in reducing the overall synthesis while maintaining a high degree of CEC value for the products.The typical multi-stage synthesis procedure is: the mixed solution was treated under microwave system at 80℃for 20min at the first step, and then to the second step under conventional system at 120℃for 2h, in the end under microwave system at 100℃for 40min.